Zeolites and process for preparation thereof

ABSTRACT

The invention relates to zeolites which have high substitution levels of element with regard to aluminium content and in particular such zeolites where the substitute to silicon ratio is also high. A method for producing such zeolites by presenting the substitute material in tetrahedral oxo-anion form is also provided.

This invention relates to zeolites and to a method of producing zeoliteshaving increased amounts of metals instead of aluminium in zeolites.

Zeolites are hydrated aluminosilicate minerals which occur naturally,but which have increasingly been made synthetically. Zeolites have athree dimensional structure arising from a framework of basic units ofSiO₄₋ ⁴ and AlO₄ ⁵⁻ tetrahedra connected through their corners of sharedoxygen atoms to form polyhedra. These basic units combine to form openframeworks containing channels and cavities in which cations and watermolecules are located.

Cations are held within the structure due to the slightly negativeoverall charge of the tetrahedra.

Much investigative work was originally carried out with syntheticzeolites to study the effect of variations in the silica/aluminiumratio. Ratios of 1600:1, i.e. silicalite and 1:1, i.e. zeolite Aresulting. Subsequently, work extended into studying the substitution ofatoms into the tetrahedra of the building blocks either in replacementof silica or aluminium. In particular, with regard to aluminium, it isknown to replace the aluminium atoms to limited extents with titanium,iron, cobalt and other metallic atoms. Replacement of silicon to limitedextents with germanium, phosphorous and other elements is also known.Such substitutions or variations are known to dramatically affect thezeolites performance both in relation to catalytic activity and/or otherproperties.

Zeolites are normally prepared from a silica source (such as sodiummetasilicate or fume silica), a source of aluminium (for instancealuminium wire or an aluminium salt) and counter cations (usually analkali metal hydroxide such as potassium hydroxide), together withwater.

There are two basic methods by which attempts have been made to replacealuminium atoms within the structure or to produce Zeolites supplementedwith other metal atoms. The first technique involves producing thealuminium/silicon zeolite in the normal manner and then strippingaluminium atoms from the structure of the crystal by chemical means;practically simultaneously metal atoms from solution are substituted into the structure. This technique allows for only limited substitution ofthe aluminium, where a significant amount of aluminium is present withinthe structure. Attempts to substitute greater than 30% of the aluminiumhave resulted in the crystalline structure of the zeolite collapsingbefore the substitute metal atoms can be incorporated within thetetrahedra. This is particularly true of types such as zeolite L.

The second technique involves the preparation of a reaction mixturecontaining aluminium, silica, water and caustic soda together with asalt of a transitional metal which competes with the aluminium duringthe zeolite's formation. This results in the substitute metal'sincorporation within the crystalline structure to a limited extent.Chlorates and nitrates of the transition metal are commonly used as thesource forms. This technique also has an upper limit of 30% or so of thealuminium being replaced as is shown for instance in PCT Application WO92/13799. Above this figure very poor crystallisation and/or poorstability of the product occurs, with the result that practicallyamorphous product results.

Thus whilst high level substitution has previously been claimed thepresent invention aims to provide a method for and materials whichactually have such high levels of substitution.

It is strongly desirable to produce zeolites containing greater than 30%or so of aluminium substitutes, such as Fe, Mn, V as these zeolitespotentially offer improved or even substantially new catalyticion-exchange and/or other properties. It is the manufacture of such highcontent substitute metal zeolites which is the problem addressed.

According to the first aspect of the invention, we provide a zeolite inwhich the Si:Me ratio is 4:1 or less (for example 3:1), where Me is anymetallic element other than aluminium and Me is introduced to thezeolite in tetrahedral oxo-anion form.

Preferably a Si:Me ratio of 4.25:1 or less (ie. 3:1, 2:1, etc) isensured. And most preferably 4:1 or less.

Preferably the aluminium to other metal ratio is between 2:1 or less, Alto other metal or metals (Al:Me).

The Al:Me ratio may be between 2:1 and 1:20.

Preferably the ratio is between 3:2 and 1:20. Most preferably between1:1 and 1:20. Ratios of 1:1 and 1:10 or 1:8 are envisaged.

The substitute metal may be iron, manganese, vanadium, or other metals,in particular transitional metals. Combinations of two or more suchmetals are also envisaged.

Preferably Si:Al is between 1:1 and 1000:1; 500:1 or; 250:1. In additionit is also preferred that the Si:Me ratio be between 4.25:1 and 1.5:1,most preferably 4:1 and 2.5:1.

The Zeolites produced may be of the composition XSi: YAl: ZMe, where Xis 2 to 2000, Y is 1 or 2 and Z is 1 to 20 and Y+Z≦X. Preferably Z≧1/4X.

Preferably X≦1000Y and most preferably X≦550Y and may be X≦250Y, 100Y,50Y, 25Y or 10Y.

Preferably Z≧Y and most preferably Z≧2Y.

According to a second aspect, we provide a zeolite made in accordancewith the method or process of the third or fourth aspects of theinvention.

According to a third aspect of the invention, we provide a method forproducing a zeolite, the method comprising providing a source of silica,a source of aluminium, and a source of water, together with a source ofone or more other metallic species, at least one of said other speciescomprising a tetrahedral oxo-anion.

We have appreciated that using species of metal ions which haveco-ordinations other than tetrahedral (as has previously invariably beendone) is prejudicial to having a high level of non-aluminium metal inthe Zeolite. This is particularly so where the metal is coordinated withnon-oxygen atoms as the metal must first lose these atoms then bind withoxygen atoms to give the preferred unit for substitution.

The species may be FeO₄ ²⁻ or MnO⁻ ₄ and, in particular may beintroduced as K₂ FeO₄ or KMnO₄.

Preferably said species has stable tetrahedral coordination for asufficient period of time under alkali conditions for said zeolite to beproduced incorporating said species. It is believed that a relativelyunstable species can be used provided it maintains tetrahedralcoordination for a time sufficient for incorporation. In this regardtime periods in excess of two hours are useful, but periods between fourand five hours are adequate. Once incorporated the surroundingcrystaline framework maintains the stability of the species. The speciesis also preferably soluble under alkali conditions.

The species is preferably provided in the regent in combination with anionic species which preferentially causes crystallisation of therespective zeolite.

The species may act by providing nucleation sites for zeolitecrystallisation.

Preferably said species is taken into said zeolite in preference toaluminium.

According to a fourth aspect of the invention we provide a process forproducing zeolites comprising providing a source of aluminium, silicon,water and one or more further metallic elements, in elemental orcompound form, wherein one or more of the further elements comprises ametallic element (other than aluminium) provided in tetrahedraloxo-anion configuration.

According to a fifth aspect, we provide a process for producing zeolitescontaining silicon, aluminium and one or more other metals, said metalsbeing present in a ratio of greater than 1:2 with respect to thealuminium content, the process comprising providing one or more of saidother metals for producing said zeolite in the reaction mixture intetrahedral oxo-anion configuration.

Preferably said metal or metals in total exceed said amount of aluminiumcontained within said zeolite crystal.

Said metal may be present in a range of ratios between 2:1 Al/Me to 1:20Al/Me.

The Si/Al ratio may be between 1000/1 and 1/1; preferably 500/1 and 2/1;most preferably 250/1 and 5:1.

Most preferably the Si:Al and Al:Me ratios are such that the Si:Me ratiois 4:1 or more (ie. 3:1, 2:1 etc).

Preferably Me is any one or more of Iron, Vanadium, or Manganese. Withregard to Iron the metal is preferably presented as a ferrate and mostpreferably as potassium ferrate.

As a result of our research we believe that the limiting factor insubstitution for aluminium is the requirement of the substitutecomponent to assume tetrahedral structure to produce the zeolite asagainst the octrahedral co-ordination of previous sources used as thesubstitute material. In this regard we believe that the incompatibilityin co-ordination of the source of Me means that the Me ions resist thetendency to be taken into and form the tetrahedral structure ofzeolites. By providing tetrahedral coordinated species this resistanceis reduced.

In producing the zeolites of the current invention we selected stablespecies of the desired metallic substitute or substitutes, in which thesubstitute atom had tetrahedral co-ordination. For many such species ahigh to very high pH may be required to achieve a sufficient period ofstability. Of course not all species may require this and the requiredpH is likely to vary from species to species.

According to a further aspect of the invention we provide a zeolite inwhich the aluminium to other metal ratio is 2:1 or less, Al to metal ormetals (Al:Me), provided that the zeolite does not have a silicon tonon-aluminium metal ratio of 4:1 or more (ie. 4.5:1).

This invention provides zeolites which were not previously possible interms of the level of non-aluminium metals present.

It is preferred that the zeolite does not have a Si:Me ratio of 3.8:1 or3.7:1 or 3.6:1 or 3.5:1 or 3.4:1 or even less, such zeolites being inexcess of those previously thought possible.

According to another aspect of the invention we provide a method forproducing a zeolite, the method comprising providing a source of silica,a source of aluminium, and a source of water, together with a source ofone or more other metallic species, at least one of said other specieshaving tetrahedral coordination, provided that said at least one of saidother species is not a tetrahedral non oxo-anion form.

With regard to substitution of iron into the structure potassium ferratewas selected. For substitution to occur the reagents selected shouldnormally be stable for at least 4 to 5 hours to allow the zeoliteproducing reaction to occur sufficiently to give rise tocrystallisation. Potassium ferrate usually requires a pH in excess of 11to give such duration of stability. At pH 13 the compound can beexpected to remain stable for several days.

During tests carried out on zeolite L, chosen because of its potassiumpreference for crystallisation, a variety of amounts of potassiumferrate were used in substitution for aluminium wire. Other forms ofFerrate may be selected to produce other Zeolites. The resultingzeolites displayed highly crystalline. and stable structures, butincorporated 75% and even up to 81% substitution of Fe atoms foraluminium atoms, (1:3; Al:Fe). We believe that no-one has achievedcomparable levels of substitution.

In similar tests, for example on zeolite L, zeolites incorporating over50% Manganese were produced, well in excess of the previous limit of 25%substitution. Potassium manganate, KMnO₄, prepared according to themethod given in "Practical Inorganic Chemistry" Pass and Sutcliffe, Pub.Chapman and Hall was used. Such substitution techniques are believed tobe particularly suitable for zeolites which use a cation as a template.

The resulting zeolites were analysed by a variety of ways to determinetheir structure and composition. X-ray diffraction showed that the unitcell size of the zeolite increased almost linearly with the increase iniron present in the solution, supporting the fact that the iron wastaken up into the zeolite.

Fourier transformation infra-red studies confirmed that the expected Febonds, in tetrahedral form were present within the zeolites produced.Thus previously unobtainable levels of substitution and extents of ironincorporation have been obtained and demonstrated.

The size, shape and general morphology of a zeolite are known to affectcatalytic performance, as is a change in the electronegativity of azeolite. Substitution of Iron into a zeolite is expected to reduce itselectronegativity based on theoretical prediction and given results fromlower levels of substitution, as well as significantly altering itsmorphology. Such zeolites can be made according to this invention.

Specific further examples, test results and conclusions follow andrelate to the inventive concept previously described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table detailing reagent amounts for experiments to replacealuminum in crystalline zeolite LTL by Fe³⁺ ;

FIG. 2 is a graph illustrating crystallization curves for Al-LTL andAl(Fe)-LTL samples plotted against time;

FIG. 3 is a table detailing the comparison of cell dimensions and unitcell volume for LTL and iron substituted samples;

FIG. 4 is a graph showing the increase in interplanar spacing forhkl(100) with increased replacement of Al³⁺ ;

FIGS. 5(a)-5(c) show SEM micrographs of Al-LTL and iron substitutedsamples;

FIG. 6 is a table of I.R. bands exhibited by pure LTL and ironcontaining LTL in the region of 1200 to 400 cm¹⁻ ;

FIG. 7 is a graph of the infrared asymmetric Si-O-T stretching regionshowing peak shift to lower wave number and development of shoulder atapproximately 975 cm⁻¹ on increased Fe³ + framework substitution;

FIG. 8 shows a typical t.g.a./d.t.g.a. trace for LTL zeolite;

FIG. 9 is a table detailing percentage weight loss with increasingtemperature for Al-LTL and Al(Fe)-LTL samples during thermogravimetricanalysis;

FIG. 10 is a table of oxide compositions of crystalline samples obtainedby semi-quantitative XRF analysis; and

FIG. 11 is a table showing the comparison of starting gel and productFe₂ O₃ and Al₂ ₃ mole fractions.

Potassium ferrate, as a primary source of iron, has been investigatedand proven in this invention in the hydrothermal synthesis of zeoliteLTL. In this example crystalline material with Fe(111) incorporated intolattice sites was isolated from starting gels containing up to 0.825mole fraction Fe₂ O₃ /Al₂ O₃. The use of basic, tetrahedral iron specieshas extended previous maximum substitution levels. X-ray diffraction,infrared spectroscopy, chemical analysis, and electron microscopyprovide evidence for the presence of framework iron. The development ofnew, i.r. absorption bands in the asymmetric and symmetric Si-O-Tstretching region, and the shift to lower wavenumbers is accompanied byan increase in the interplanar spacings and unit-cell dimensions withincreased Al³⁺ replacement. A change in morphology is also observed.

The isomorphous replacement of Al or Si in the zeolite framework byheteroatoms produces new materials with significantly modifiedphysicochemical and catalytic properties. Chu, C. T., and Chang, C. D.J. Phys. Chem. 1985, 89, 1569; Dwyer, J., and O'Malley, P. J., Stud.Surf. Sci. Catal. 1987, 35, 219; Borade, R. B. Zeolites 1987, 7, 398!.These materials have the potential to carry out petrochemical and/ororganic reactions. John, C. S., Clark, D. M., and Maxwell, I. E. inPerspective in Catalysis (Eds. J. M. Thomas and K. I. Zamaroev) 1UPAC,1991, 387; Holdericj, W. F., Hesse, M., and Maumann, F. Agnew. Chem.Int. Ed. Engl. 1988, 27, 226!. The use of iron (111) as a substitutingelement has been reviewed recently. Ratnasamy, P., and Kumar, R. Catal.Today 1991, 9(4), 329!. The Fe³⁺ ion has a larger ionic radius (0.63A)than Al³⁺ (0.53A), and its tendency to form insoluble hydroxides in abasic environment and ability to change oxidation state has presentedmany synthetic problems. Despite this, ferrisilicate analogues of manyzeolites, e.g., ZSM-5, Y, beta, and mordenite, have been prepared andcharacterised successfully but with only low levels of substitution andlow total amounts of Fe present in the zeolite structure.

In this example the synthesis of crystalline LTL zeolite in which up to0.825 mole fraction Al₂ O₃ has been replaced by Fe₂ O₃ in the frameworkis demonstrated. This has been achieved using potassium ferrate (K₂FeO₄). The use of ferrate(VI) in impregnation, i.e., secondary synthesisand surface treatment has been widely documented, but it seems that FeO₄²⁻ as a source of framework iron is relatively unexplored. Barrer, R.M., and Cole, J. F. U.S. Pat. No. 3,674,709, Air Products (1972)!. TheFeO₄ ²⁻ ion, which is moderately stable in strongly alkaline media andhas tetrahedral geometry (isostructural to Al (OH)₄ -), has been foundby us to encourage the nucleation of zeolite species. A maximum level ofsubstitution of 0.3 mole fraction in LTL has been reported previously.Joshi, P. N., Awate, S. V., and Shiralkar, V. P. J. Phys. Chem. 1993,97(38), 9749!.

Potassium ferrate (K₂ FeO₄) was prepared using the method outlined byAudette and Quail. Aidette, R. J., and Quail, J. W. Inorg. Chem 1972,11(8), 1904!. Fine aluminium powder (GPR supplied by BDH chemicals),fumed silica (98% CAB-O-SIl M5 BDH Scintran), and potassium hydroxidepellets (GPR-Scientific and Chemical Supplies Ltd., Bilston, WestMidlands) were used as supplied together with deionised water.

The starting molar composition was:

    9K.sub.2 O.xFe.sub.2 O.sub.3.(1-x)Al.sub.2 O.sub.3.2OSiO.sub.2.315H.sub.2 O

where x=0, 0.25, 0.5, 0.75, 0.90 and 1. The reagents amounts for eachexperiment are given in the table below.

    ______________________________________    X      0.0     0.25    0.5   0.75   0.90  1    ______________________________________    KOH    25.44   23.94   22.44 20.96  20.08 19.50    Al     1.36    1.02    0.67  0.34   0.13  0.0    K.sub.2 FeO.sub.4           0.0     2.48    4.95  7.40   8.86  9.83    SiO.sub.2           30.26   30.16   30.04 29.94  29.87 29.83    H.sub.2 O           142.94  142.40  141.90                                 141.36 141.06                                              140.84    Total  200     200     200   200    200   200    ______________________________________

The reaction mixture was prepared by dissolving potassium hydroxide in˜35 cm³ of deionized water and carefully adding any aluminium powder insmall aliquots. The solution was then allowed to cool for 20 min beforeaddition of any sold K₂ FeO₄ while stirring. The purple solution wasthen added slowly to silica slurried in ˜105cm³ of water and mixedthoroughly by hand to a smooth, purple paste. A slight increase intemperature and thickening of the reaction mixture was observed. The pHtaken at this time was between 13.5 and 14.0. The gel was sealed in PTFEbottles (75 cm³) and heated statically at 100±1° C. No intentionalseeding or aging was carried out. Samples were removed and cooledperiodically, 24 hour intervals in most cases, 48 hours for 0.75 and 0.9tests and solid products were separated from the mother liquor byBuchner filtration. The samples were then washed with deionized water(3×30cm³) and heated overnight at 40±1° C. in a drying oven.

Solid products were characterised using conventional techniques. Thecrystallinity of materials was determined from XRD patterns recorded ona Philips 1710 X-ray diffractometer using CuKα radiation. The sampleswere compared by computerised on-line isotypical search with the JCPDSstandard 39-224 (K₆ Na₃ Al₉ Si₂₇ O₇₂ 21H₂ O). The size, shape, andmorphology of the zeolite crystals were examined using a scanningelectron microscope (Philips 515) after coating with gold-evaporatedfilm on an aluminium peg. The framework i.r. spectra reported are forhydrated zeolites supported in alkali halide wafers. The samples (0.5mg) were uniformly mixed with 200 mg of dry KBr (BHD SpectrosoL) andground by hand in a pestle and mortar for 5 min. The mixture was thenpressed at 9 tons to give a transparent fused halide window (13 mmdiameter). Spectra were recorded in air at room temperature on a PhilipsPU9624 FTi.r. spectrophotometer. Thermogravimetric analysis wasperformed on a Mettler TG50 thermobalance/Mettler TA3000 processor undernitrogen at a heating rate of 20 K min ⁻¹ using ˜15 mg of sample.Chemical composition was determined on an ARL 8410 X-ray spectrometerusing the ARL semiquantitative analysis package. The samples (0.3 g)were accurately weighed and sandwiched between X-ray transparent film(Mylar). Results were calculated as oxides from the stoichiometry.

The replacement of aluminium in crystalline zeolite LTL by Fe³⁺ wasattempted systematically. The starting molar composition was:

    9 K.sub.2 O.xFe.sub.2 O.sub.3.(1-x) Al.sub.2 O.sub.3.20 SiO.sub.2.315H.sub.2 O

where x=0,0.25, 0.50, 0.75, 0.825, 0.90, and 1.0.

The reagent amounts for each experiment are given in FIG. 1.

Fully crystalline LTL zeolites were obtained in this example fromsystems containing up to x=0.825 Fe₂ o₃. These materials werewhite/cream in colour and showed good pattern matching to standard39-224 by X-ray diffraction. The products from systems containing 0.90and 1.00 mole fraction were amorphous, brown solids. Joshi et al. Joshi,P. N., Awate, S. V. and shiralkar, V. P. J. Phys. Chem. 1993,98(38),9749! reported a maximum level of substitution of x=0.3 using iron (111)nitrate Fe(NO₃)₃.9H₂ O! as a source of iron. They claimed that abovethis level the larger Fe--O bond length compared with Al--O inhibitedthe formation of the cancrinite cage (submit of LTL). Our resultssuggest that much greater substitution is possible, provided that theiron is available in the starting gel in a suitable form.

The kinetics of crystallization were followed by XRD measurements on thewashed, dry solids. The percentage crystallinity was calculated by theratio of the sum of the most intense reflectances of the sample to thatof the most crystalline reference. In general, the rate ofcrystallization decreased with increasing iron concentration in the gel,behavior recognized by Joshi (FIG. 2). We confirm that both theinduction period (nucleation) and the time taken to reach maximumcrystallinity were extended at higher levels. it was noted that all theXRD reflections for iron-substituted samples were shifted to higher dvalues compared with AL-LTL. The positions hk(100), the most prominentpeak, for each crystalline zeolite are shown in FIG. 4. This shift wasaccompanied by an overall increase in the unit-cell parameters, celldimensions and volume, with increased Al³⁺ replacement (FIG. 3). Thisprogressive increase is significant evidence for framework incorporationof iron.

SEM micrographs of the Al-LTL and the iron-containing samples indicategood quality crystals of even distribution and no amorphous material.The crystals were generally very small in size (˜1 μm or less). Adistinct change in morphology is also observed on increasing the ironcontent (FIG. 5).

The crystals can be described as "platelet" shaped, cylindrical with alength/diameter ratio of ˜0.5. The Al-LTL samples have a domed basalplane with a series of steps or terraces. The iron-substituted crystalshave basal planes of increasing flatness and become more"ice-hockeypuck" shaped with increased aluminium replacement (FIG.5a-c).

This morphological effect has been recognized by Verduijn Verduijn, J.P. Int. pat. W092/13799, Exxon Chemicals (1992)! for aluminosilicateK-LTL from a synthesis gel containing up to 0.06 Fe₂ O₃ /Al₂ O₃ . Ageneral decrease in crystal size on increased iron substitution was alsorecorded. Zeolite LTL is used as a catalyst in the reforming ofhydrocarbons, especially the aromatization of paraffins. Verduijndemonstrated that a Pt-loaded, iron-containing LTL catalyst withice-hockeypuck morphology showed significantly improved selectivity andstability over standard, commercial zeolite K-(Al)LTL. Hammer Hammer,International Journal of Energy Research, Vol.18, 223-231(1994)! havedemonstrated the significance of Fe load and the likelyhood of increaseactivity, both catalytic and ion-exchange, if such levels could beachieved. Therefore, the presence of framework iron in the zeolite andthe flatness of basal planes are an indication of the intrinsiccatalytic quality of the crystals.

The i.r. spectra of zeolite LTL and its iron-containing analoguesclosely agree with the literature Flanigen, E. M., Khatami, H., andSzymanski, H. A. Molecular Sieve Zeolites, Adv. Chem. Ser., AmericanChemical Society, Washington, D.C., 1971, 101,201-229!. Thecharacteristic absorption bands are assigned in FIG. 6. It can be seenthat the Si-O-T asymmetric and symmetric stretching vibrations and theT-O bend shift progressively to lower wavenumbers on increasing ironcontent in the gel. Further evidence for framework siting of Fe atoms issuggested by the observations of a band (shoulder) at around 978 cm⁻¹,which is absent in the i.r. spectrum of pure Al-LTL. The relativeintensity of the sholder at 978 cm⁻¹, increases with increasing ironcontent, as shown in FIG. 7.

A typical t.g.a./d.t.g.a. trace is shown in FIG. 8.

The sharp, endothermic weight loss at ˜120° C. is characteristic ofLTL-type zeolites. This peak corresponds to the desorption/dehydrationof physically absorbed water molecules. The peak temperature and thepercentage weight loss decrease slightly on increased iron substitution(FIG. 9). This suggests that samples containing iron are morehydrophobic and that the occluded water is less strongly bound. Thereduced water content is not unexpected. Due to the larger size of theFe(111) ion, a greater charge delocalization may be possible. This wouldlead to lower polarizing power at the iron sites over those containingaluminium.

Bulk chemical analysis of crystalline material was carried out usingX-ray spectroscopy. Elemental composition expressed as oxides, and molefractions of Fe₂ O₃ and Al₂ O₃ for the starting gel and products aregiven in FIGS. 10 and 11. A steady increase in the Fe₂ O₃ /Al₂ O₃ ratioon increased Fe content of the reaction gel can be seen. This indicatespreferential up-take of iron, over aluminium, into the structure. Thereis also a corresponding decrease in percentage SiO₂. In all cases the K₂O/(Al₂ O₃ +Fe₂ O₃) ratios were slightly higher than expected. This maybe due to insufficient washing at the isolation stage.

Iron (111) framework-substituted LTL zeolite has been prepared with upto 0.825 mole fraction Al₂ O₃ replaced by Fe₂ O₃. The use of basic,tetrahedral FeO₄₋ ²⁻ ions as a source of Fe³⁺ has extended previoussubstitution levels. The nucleation of zeolite species and the formationof the cancrinite cage is therefore possible at values of x>0.3. Allcrystalline products were white/cream in colour, indicating the absenceof occluded oxides, and the mother liquors were colourless.

Evidence for lattice incorporation was obtained from XRD. All samples,Al-LTL and Al(Fe)-LTL, showed excellent pattern matching to standard39-224. Increased Al³⁺ replacement resulted in a notable peak shift toincreased d spacings, and larger unit cell parameters (dimensions andvolume) were observed, reflecting the larger size of the Fe³⁺ ion. Thei.r. stretching vibrations of the Si-O-T move progressively to lowerwavenumbers on increased iron(111) incorporation. The development of anew band at ˜975cm⁻¹ that is absent from the i.r. spectrum of pure LTLand becomes more intense at higher iron concentrations is also a goodindicator of lattice substitution.

Chemical analysis of the samples showed increased Fe₂ O₃ /Al₂ O₃content, and the ice-hockeypuck morphology associated withiron-containing K-LTL zeolite was evident from electronmicroscopy.

We claim:
 1. A process for producing a zeolite comprising the stepsof:(a) providing a source of aluminum (Al) dissolved in a metalhydroxide solution; (b) introducing a source of at least one metallicelement (Me) other than aluminum in tetrahedral oxo-anion form to themetal hydroxide solution; (c) mixing the metal hydroxide solution with asource of silicon (Si) slurried in water; and (d) subjecting the mixtureto conditions suitable to cause a reaction which forms a zeolite;wherein said Me source is selected from the group consisting of FeO₄ ²⁻and MnO₄ ⁻.
 2. A process according to claim 1 wherein the step ofintroducing said Me further comprises introducing said Me in combinationwith an ionic species having nucleation sites for causingcrystallization of the resulting zeolite.
 3. A process according toclaim 1 wherein the ratio of said Si to said Al (Si:Al) is less thanabout 1,000 to 1 (1,000:1) and greater than about 1 to 1 (1:1).
 4. Aprocess for producing a zeolite comprising the steps of:(a) providing asource of aluminum (Al) dissolved in a metal hydroxide solution; (b)introducing a source of at least one metallic element (Me) other thanaluminum in tetrahedral oxo-anion form to the metal hydroxide solution;(c) mixing the metal hydroxide solution with a source of silicon (Si)slurried in water; and (d) subjecting the mixture to conditions suitableto cause a reaction which forms a zeolite; wherein the ratio of said Meto said Al (Me:Al) is greater than about one to two (1:2); and whereinsaid Me source is selected from the group consisting of FeO₄ ²⁻ and MnO₄⁻.
 5. A process according to claim 4 wherein the step of introducingsaid Me further comprises introducing said Me in combination with anionic species having nucleation sites for causing crystallization of theresulting zeolite.
 6. A process according to claim 4 wherein the ratioof said Si to said Al (Si:Al) is less than about 1,000 to 1 (1,000:1)and greater than about 1 to 1 (1:1).
 7. A process according a zeolitecomprising the steps of:(a) dissolving potassium hidroxide in deionizedwater; (b) introducing aluminum powder to the potassium hidroxidesolution; (c) cooling the potassium hidroxide solution; (d) introducingsolid potassium ferrate to the cooled potassium hidroxide solution; (e)mixing the potassium hydroxide solution containing the dissolvedaluminum powder and the dissolved potassium ferrate with a slurry ofsilica and water; (f) heating the mixture statically at about 100° C.;(g) cooling the mixture; (h) filtering the solid product from themixture; (i) washing the filtered solid product in deionized water; and(j) driving the filtered and washed solid product for at least 12 hoursat about 40° C.